Induction cooking appliance including cooking vessel having means for transmission of temperature data by light pulses

ABSTRACT

Herein disclosed is an induction cooking/warming appliance wherein an induction coil is located below a vessel supporting means, such as a counter. The counter may have a passage therethrough for the transmission of light, or it may be a solid body of transparent or translucent material. A double-walled vessel for containing food to be cooked or warmed is provided. The vessel is supportable on the counter. An inner wall of the vessel is inductively heated by a main magnetic field produced by the induction coil; but, an outer wall of the vessel, which is in contact with the counter on which the vessel is supported, is not inductively heated. Moreover, the outer wall of the vessel transmits light. Included within the vessel between the two walls thereof is a temperature detection unit which includes a temperature sensor unit arranged for sensing the temperature of the inner wall of the vessel and means responsive to the magnetic field produced by the induction coil for energizing an LED to produce light pulses at a rate corresponding to the temperature sensed by said temperature sensor unit. These light pulses are transmitted through the outer wall of the vessel and either through the counter or through a passage in the counter to a temperature receiving unit which includes a photodetector which is instrumental in developing a signal representative of the temperature of interest. Various embodiments of the vessel and the components thereof are disclosed.

United States Patent 1 1 1111 3,742,174

Harnden, Jr. 1 June 26, 1973 INDUCTION COOKING APPLIANCE [57] ABSTRACTINCLUDING COOKING VESSEL HAVING Herein disclosed is an inductioncooking/warming ap- MEANS FOR TRANSMISSION OF pliance wherein aninduction coil is located below a TEMPERATURE DATA BY LIGHT PULSESvessel supporting means, such as a counter. The

75 Inventor; John Hal-den, Jr" Schenectady counter may have a passagetherethrough for the transy mission of light, or it may be a solid bodyof transparent or translucent material. A double-walled vessel for con-[73] Asslgnee: Genera] Electnc Cmnpany taining food to be cooked orwarmed is provided. The Schenectady vessel is supportable on thecounter. An inner wall of 22 Filed; 29 1971 the vessel is inductivelyheated by a main magnetic field produced by the induction coil; but, anouter wall [21] Appl' 213,336 of the vessel, which is in contact withthe counter on which the vessel is supported, is not inductively heated.

52 us C] n 219 1049 219 1077 2 9 502 Moreover, the outer wall of thevessel transmits light.

220/9 R 350/333 H 33 32 Included within the vessel between the two walls[51] Int. Cl. H05b 5/04 thereof is a temperature demmion unit whichincludes 58 Field of Search 219/1044, 10.75,atemperaturesensorunitarranged forsensingthe 219 1 77 1079 433 441 502;250/333, H perature of the inner wall of the vessel and means re- 05215; 356/43, 3 5 1 9; 220 9 sponsive to the magnetic field produced bythe induc- 33 23 2 DIG 2; 33 3 tion coil for energizing an LED toproduce light pulses at a rate corresponding to the temperature sensedby 5 References Cited said temperature sensor unit. These light pulsesare UNITED STATES PATENTS transmitted through the outer wall of thevessel and either through the counter or through a passage in the g zcounter to a temperature receiving unit which includes 3 6l9 6l2 11 1971Belkeixiiii 250/83.Ii H *Photodetecwr which is instrumemal in develqinga 3/1959 Baker I I 336/82 signal representatlve of the temperature ofmterest. 2,133,494 10/1938 Waters 219 1049 Various embodiments of thevessel and the p 3,530,499 9/1970 Schaoeder 219/1049 nents thereof aredisclosed 3,449,629 6/1960 Wigert et al. 219/502 XR Primary ExaminerJ.V. Truhe 12 Claims, 9 Drawing Figures Assistant ExaminerB. A. ReynoldsAttorney-John F. Ahern, Patrick D. Ward et al.

TEMPERATURE -sr1mc POWER CONVERSION cmcun' s A.C. SOURCE PATENlEflJlmzsms TEMPERATURE SIGNAL PROCESSING cmcum g 44 souo STATE INVERTER l---sTAT|c POWER RECTIFIER 1 CONVERSION CIRCUIT 4;

A.C. SOURCE PAIENIED JUII 26 I975 mo mmpzmwasmk FREQUENCY OF LIGHTPULSES 64 VCO 2 TEMPERATURE DETECTION UNIT I l I I J SIGNAL PROCESSINGTEMPERATURE CIRCUIT i I L TEMPERATURE RECEIVING UNIT 46x, RECTIFIERSTATIC POWER CONVERSION UNIT RECTIFIER g LOAD UTILIZATION MEANSINDUCTION COOKING APPLIANCE INCLUDING COOKING VESSEL HAVING MEANS FORTRANSMISSION OF TEMPERATURE DATA BY LIGHT PULSES CROSS REFERENCES TORELATED APPLICATIONS A fuller appreciation of induction cookingappliances, generally, as well as some of the sophistications which maybe embodied therein is to be had by referring to the following U.S. Pat.applications: Ser. No. 200,526, filed Nov. 19, 1971, in behalf of DavidL. Bowers et al. titled SOLID STATE INDUCTION COOKING APPLIANCE; Ser.No. 200,424, filed Nov. 19 1971, in behalf of JD. I-larnden, Jr. et al.,titled SOLID STATE INDUCTION COOKING APPLI- ANCES AND CIRCUITS. Theentire right, title and interest in and to the inventions described inthe aforesaid patent applications, as well as in and to the aforesaidapplications, and the entire right, title and interest in and to theinvention hereinafter described, as well as in and to the patentapplication of which this specification is a part, are assigned to thesame assignee.

BACKGROUND OF THE INVENTION This invention pertains to induction cookingor warming appliances, in general; and, in particular, to a novel foodprocessing vessel especially suitable for use in conjunction withinduction appliances of the aforesaid type, the novel vessel provided bythe invention having incorporated therein means for extracting electricpower from the main induction field of the appliance for the purpose ofproducing local power for use by load utilization means in the vessel.

An important aspect, among others, of the present invention is theprovision of a novel food processing vessel suited for use withinduction appliances of the aforesaid type wherein said vessel includesa temperature detection unit which includes the aforesaid means forextracting electrical energy from the main induction field of theappliance for the purpose of initiating the wireless transmission oftemperature data by means of light pulses radiated from the vessel to areceiving unit which may be remotely located elsewhere on the appliance.

Prior art electric ranges (i.e., those employing resistance heatersurface elements) and gas ranges present a number of problems withrespect to temperature sensing. With such prior art ranges the approachmost often employed is to directly sense the temperature of the vessel.For this purpose a contact-type temperature sensor unit is usuallyemployed; i.e., the temperature sensor unit is positioned so that it isin direct contact with the cooking vessel being heated. The vesselsinvolved are usually fabricated from cast iron, stainless steel, copperor copper-clad stainless steel, etc. These vessels are consideredconventional and are abundantly available. Temperature sensing as donein the prior art has not proved entirely satisfactory for, among others,the following reasons:

First, with prior art electric and gas ranges the pri- -mary heatingsource (e.g., the surface mounted electrical resistance coils or the gasfed flames) spuriously heats the temperature sensing unit and, moreover,other heated parts of the range thermally perturb the temperaturesensing unit as well.

Second, in prior art electric and gas ranges because of the relativelyhigh temperatures involved, principally because of the nature of theprimary heating source and its proximity to the vessel-contactingtemperature sensor, the materials from which the temperature sensingunits and their associated components may be fabricated are ratherrestricted.

Third, in prior art electric and gas ranges, principally because of thehigh temperatures occasioned by the nature of the primary heating sourceand its proximity to the contact-type temperature sensing unit extensivethermal shielding, or insulation is required.

Fourth, in prior art electric and' gas ranges because of the severethermal stresses created in the vesselcontacting temperature sensingunit, as a consequence of the high temperatures occasioned by the natureof the primary heating source and its proximity to the temperaturesensing unit, relatively massive and sophis ticated as well as somewhatmechanically complex spring arrangements and structures were requiredfor the purpose of maintaining adequate contact between the temperaturesensing unit and the cooking vessel.

The four problems, hereinbefore mentioned, are discussed in greaterdetail hereinafter.

In prior art electric and gas ranges the temperature sensing means andits associated components are directly heated, spuriously, in somemeasure by a high temperature primary heating source. For example, inthe conventional electric range a temperature sensing unit is located atthe center of a spirally wound resistance heating coil. This heatingcoil and the tempera ture sensing unit are both mounted on the top orworking surface of the range counter. A cooking vessel rests on andcontacts the heating coil as well as the temperature sensing unit.Although the temperature sensing unit directly contacts the heatedcooking vessel, it is also subjected to direct spurious heating by theranges heating coil; e.g., by radiation and convection. In addi tion,the temperature of the temperature sensing unit is influenced by, amongother things, the metallic counter of the electric range. Similarly in agas range, the flames directly heat the temperature sensing unit.Moreover, heated metallic gridirons as well as the heated metalliccounter top thermally influence the temperature sensing unit.

Also, in prior art electric and gas ranges, because of the nature of theprimary heating sourceand its proximity to the temperature sensing unit,various component parts of the temperature sensing unit have to befabricated with materials which are capable of withstanding relativelyhigh temperatures; e.g., approximately I,400Fl,600F. For example, in theconventional prior art electric range wherein the temperature sensingunit is located at the center of the spiral resistance heating coilwhich is, in turn, mounted on the metallic counter top of the range, thetemperature sensing unit and its associated components are subjected tothe elevated temperatures hereinbefore set forth. Significant thermalstresses are, as a result, induced in the temperature sensing unit aswell as in its associated components. Similar conditions occur in gasranges.

In prior art electric and gas ranges, principally be cause of the natureof the primary'heating source and its proximity to the temperaturesensing unit contacting the cooking vessel, the temperature sensing unitas well as its associated components are required to have extensivethermal shielding, or insulation, for the purpose of minimizing theinfluences of spurious heating by the high temperature heating source aswell as by the metallic range counter and metallic gridirons. Withoutsome effective thermal shielding or insulation, the temperature sensingunit will provide a false indication of temperature unless temperaturecompensation is appropriately applied. However, such compensation is notfeasible because of the wide range of cooking conditions. For example,it is very difficult to achieve a system in which both steady-state andtransient, or dynamic, compensation is easily achieved. In any event,cooking performance is compromised. Moreover, without effective thermalshielding severe thermal stresses induced in the various component partsof the temperature sensing unit will cause a disabling, or sometimesdestruction, of the temperature sensing unit.

The prior art temperature sensing units, especially those which areemployed with the prior art electric ranges for the purpose ofcontacting the cooking vessel, are generally massive and are of a rathersophisticated and somewhat mechanically complex structure andarrangement. The high temperature environment within which thetemperature sensing unit is located permits severe thermal stresses tobe induced in the various components of the temperature sensing unit.These stresses tend to promote warping of the various components. Forexample, because of the aforesaid thermal stresses, a relatively massivedouble-spring arrangement is usually employed in combination with atemperature responsive device. The temperature responsive device, actingagainst spring restraint, contacts the bottom surface of the cookingvessel. The vessel rests on a flat spiral heating coil disposed on thetop surface of the range counter. The massive double-spring arrangementis rather stiff and this is due in large part to the need to make thearrangement structurally resistant to thermal deformation. Such a springarrangement generally functions satisfactorily to enable the temperaturesensing unit to contact a relatively smooth flatbottom surface of arelatively heavy cooking vessel such as a cast iron pot containingfoodstuff to be cooked. Being in contact with the surface of the vessel,it is conceptually possible for the temperature sensing unit to detectthe temperature of the vessel. However, in the event that a relativelylight weight pot is used or if a pot having a rather irregularlycontoured bottom surface is used, such prior art contact typetemperature sensing units employing the aforesaid stiff springarrangement proved unsatisfactory. For example, if a cooking vessel isused which is not sufficiently heavy, there will be an insufficientweight to adequately compress the spring arrangement. One consequencewill be that the vessel will not rest on the resistance heating coil inthe most intimate contact possible therewith. The cooking vessel will,as a result, be raised or tilted and thereby make for inefficient heattransfer between the resistance heating coil and the vessel. Inaddition, a prior art contact-type sensor unit could not, obvi ously, beapplied to a double-walled cooking vessel where no relationship existsbetween inner and outer wall temperatures; i.e., no relationship betweenthe cook surface temperature and the outer wall temperature. Secondly,physical space or clearance resulting with vessels having feet whichrest on counter tops in prior art ranges would require sensors havingsprings to make conventional temperature sensing heads travel ratherlarge distances.

SUMMARY OF THE INVENTION Although the invention is hereinafterdescribed, and illustrated in the accompanying drawings, as beingemployed in conjunction with an induction range it is, nevertheless, tobe understood that the inventions applicability is not limited toinduction cooking or warming ranges but may be embodied in, for example,portable counter top warming or cooking appliances, such as warmingtrivets, as well as in other types of induction heating apparatus whichneed not, necessarily, be used for cooking or warming food.

One object of the present invention is the provision of a vessel for usewith an induction range, said vessel including means for extractingelectrical energy from the induction coil of the range for providinglocal power for load utilization means or local power for signal energy,such as signal energy for the wireless transmission of temperature datafrom the vessel to a remotely located receiver.

Another object of the invention is the provision of an inductioncooking/warming appliance including a cooking/warming vessel, saidappliance including a temperature sensing unit for sensing or detectingthe temperature of cooking/warming vessel or utensil being heated.

Another object of the invention is the provision of an inductioncooking/warming appliance including the aforesaid temperature sensingunit wherein said sensing unit is free from spurious heating.

Another object of the invention is the provision of an inductioncooking/warming appliance including the aforesaid temperature sensingunit, the materials of fabrication of said temperature sensing unit notbeing restricted by the elevated temperatures heretofore encountered inprior art electric and gas ranges.

Another object of the invention is the provision of an inductioncooking/warming appliance including the aforesaid sensing unit, saidtemperature sensing unit not requiring the thermal insulation orshielding in the ways or to the extent heretofore employed in prior artelectric and gas ranges.

Another object of the invention is the provision of an inductioncooking/warming appliance including the aforesaid temperature sensingunit, said temperature sensing unit being capable of accurately sensingthe temperature of the vessel regardless of the weight of the vesseland/or the weight of the food therein and/or regardless of whether thevessel has or has not an irregular outer surface or contour; saidtemperature sensing unit not requiring the prior art spring constructionor arrangement.

Another object of the invention is the provision of an inductioncooking/warming appliance including a temperature sensing unit which canaccurately detect the temperature of the vessel regardless of the factthat the vessel may have an outer wall which is thermally nonconductive.

Another object of the invention is the provision of an inductioncooking/warming appliance including the aforesaid temperature sensingunit for sensing the temperature of a vessel being heated; said vesselbeing supported by a vessel supporting means having an uninterruptedworking surface.

Another object of the invention is the provision of an inductioncooking/warming appliance including wireless means for transmittingtemperature data from the vessel to a location which is relativelyremote from the vessel.

Another object of the invention is the provision of an inductioncooking/warming appliance including wireless means for transmittingtemperature data from a vessel being heated to a location remotetherefrom; said wireless means being powered by a portion of the maininduction field which is employed for heating the vessel.

Another object of the invention is the provision of a novelcooking/warming vessel which is adapted for being inductively heated aswell as for initiating the wireless transmission of temperature data bymeans of light pulses radiated from the vessel to a relatively remotelocation.

The invention, hereinafter described and illustrated in the accompanyingdrawings, enables the achievement of the aforementioned objectives, aswell as others, in that there is provided an induction cooking orwarming appliance and a vessel adapted for being inductively heated. Thevessel includes a portion in which heating current may be induced forthe purpose of heating said portion as well as food contained withinsaid vessel. The cooking appliance is comprised of a vessel supportingmeans in which no substantial heating current is induced when thesupporting means is subjected to a changing magnetic field. The vesselsupporting means includes a surface which is adapted for supporting thevessel. Advantageously, the aforementioned surface of the vesselsupporting means may be an uninterrupted surface which may also serve asa working surface for the preparation of food, among other things. Thecooking appliance is provided with an induction coil which isenergizable from a suitable power source so as to provide a changingmagnetic field of at least ultrasonic frequency. The changing magneticfield causes heating current to be induced in the aforementionedinductively heatable portion of the cooking vessel. As a result, foodcontained within the vessel may be heated. Also provided is atemperature sensing unit which is comprised of a temperature detectionunit and a temperature receiving unit. Briefly, the temperaturedetection unit is incorporated in the vessel and said unit derives powerfrom the aforementioned changing magnetic field produced by the remoteinduction coil. With the power thus derived, the temperature detectionunit is enabled to transmit temperature data acquired by a temperaturesensor unit located in the vessel by means of light pulses to atemperature receiving unit which may be remotely located elsewhere onthe cooking appliance. The temperature receiving unit includes aphotodetector which is coupled with a temperature signal processingcircuit. Temperature data received by the receiving coil is processed inthe temperature signal processing circuit and a signal is developedwhich is representative of the temperature of interest.

One feature of the invention resides in the transmission of temperaturedata by means of light pulses from a temperature detection unit to aremotely located temperature receiving unit. Since such transmission ismade by means of light pulses no interference, or crosstalk, from themain field produced by the induction coil occurs.

Another feature of the invention resides in the provision of a novelcooking/warming vessel in which there is incorporated various electricaland electronic components; i.e., those components of which thetemperature detection unit is comprised.

Other objects and features, as well as a fuller understanding of theinvention, will appear by referring to the following detaileddescription, claims and drawings.

. DESCRIPTION OF DRAWING FIGURES FIG. 1 is a perspective view of aninduction cooking range showing the top or working surface thereof onwhich there is supported a cooking vessel.

FIG. 2 is an enlarged cross section view as viewed along the sectionline 2-2' in FIG. 1. Also shown is block diagram of, among other things,an induction coil and power and control circuitry associated therewith.

FIG. 3 is a fragmentary cross section view showing an alternativeconstruction of the range counter employed with the induction cookingrange of the present invention.

FIG. 4 is a cross section view similar to the view shown in FIG. 2 butshowing a modification of the cooking vessel employed with the presentinvention.

FIG. 5 is a fragmentary cross section view showing an enlargement of aportion of the view shown in FIG. 4.

FIG. 6 is a graph showing the detected temperature of the cooking vesselemployed herein as a function of the frequency of light pulses emittedby a light emitting diode (LED).

FIG. 7 is a block diagram showing the overall electronic and electricalsystem of the induction cooking or warming system according to theinvention.

FIG. 8 is a fragmentary view showing an alternative way of extractingpower from the main induction field produced by the ranges inductioncoil, the extracted power being employed for providing signal energy forthe transmission of temperature data by light pulses.

FIG. 9 is a diagrammatic illustration showing how energy extracted fromthe main induction field by extraction means within the vessel may beemployed for powering a load utilization means in the vessel.

DESCRIPTION OF PREFERRED EMBODIMENTS In FIG. 1 there is illustratedaperspective view of part of an induction cooking range designatedgenerally by the reference number 20. The range 20 is provided with acounter 22 which is suitably supported by a range substructure 24.Located at the rear of counter 22 and fastened to substructure 24 is aninstrument and control panel 26. On panel 26 there is mounted a numberof controls 28 and a like number of temperature indicators 30. Althoughtemperature indicators 30 are illustrated in the drawing figures asbeing dial-type thermometers, it is to be understood that other displaymeans such as digital displays of temperature or temperature ranges maybe employed. In addition, such displays may provide a visible indicationof rate of change of temperatures. On the top or working surface of thecounter 22 there is illustrated four dotted line circles. These circlessuggest locations where four cooking vessels, such as pots, pans, etc.,may be located during the cooking process.

As illustrated, a cooking vessel 34 is rested on the working or topsurface of counter 22, covering one of the dotted line circles. Belowthe counter 22 and positioned beneath each of the dotted line circlesthereon is a separate induction coil 36. Each induction coil 36 isseparated from the bottom surface of the counter 22 by an air gap. Eachinduction coil 36 is a relatively flat,

spirally wound coil which includes at the center thereof a centralaperture designated, generally, by the'reference number 38. Eachinduction coil is electrically connected as shown in FIGS. 2 and 7 tothe output of a solid state inverter 44 which, in turn, has an inputwhich is electrically connected to the output of a rectifier 46.Inverter 44 is a solid state inverter and, as combined with rectifier46, forms a static power conversion circuit designated, generally, bythe reference number 43. The rectifier 46 includes an input which iselectrically connected to a conventional A.C. source 88 which may be a60 Hz, single phase, IN) or 220 volt source. More details as to thestatic power conversion circuit 43 including the rectifier 46 andinverter 44 may be had by referring to the patent applicationshereinbefore cross-referenced.

Also shown in FIGS. 2 and 7 is one of the controls 28 which may, forexample, be a switch which is electrically coupled with inverter 44 forthe purpose of controling the flow of power therefrom to an inductioncoil 36. The control 28 is marked in degree F settings to enable thehousewife to call for a particular temperature or temperature rangeperformance. However, a temperature indicator 3% associated with aparticular control 28 provides a visible indication of the actualtemperature of vessel 34. The temperature indicator 36]) provides, inaddition, an indication of the rate of temperature rise and fall. Thisrate information is considered to be an important aspect of the cookingprocess.

The rectifier 46 may be a regulated full-wave bridge rectifier employingsolid state devices and operating to convert A.C. input power to D.C.output power. Also, the inverter 44 employs SCRs which in performance oftheir control switching function enable the inverter 44 to deliverrelatively high frequency power (ultrasonic or above) to drive or powerthe induction coil as.

As discussed in more detail hereinafter, vessel 341 has incorporatedtherein a temperature detection unit which includes means for providinglight pulse signals representative of the sensed temperature of thecooking vessel. These light pulses are received by a temperaturereceiving unit which is designated, generally, by the reference number50. (FIG. 7). The temperature receiving unit 50 includes photodetectormeans (e.g., a silicon photodiode) 541 as shown in FIGS. I4, locatedbelow the range counter 22. From temperature receiving unit 50 theaforementioned light pulses are converted to suitable electrical signalswhich are delivered to an input of a temperature signal processingcircuit 45 (FIGS. 2 and 7). The temperature signal processing circuit 45develops an output signal representative of the temperature of cookingvessel 3 and this output signal is delivered to the temperatureindicatorv 30 for display.

As indicated in FIGS. 2 and 7, temperature signal processing circuit 45includes: a first input coupled to rectifier 46 for deriving therefrom aD.C. voltage; a second input in the form of a pair of electricalconductors which extend from the photodetector means 5d of temperaturereceiving unit 50; and, an output comprising a pair of conductorsdirectly connected to the temperature indicator 30.

In the cross section view of FIG. 2 one embodiment of the cooking vessel34 according to the invention is illustrated. As shown, the vessel 34 iscomprised of an outer cup, or cup-like member, 7%. Nested within theouter cup 70 is an inner cup 7ll. Atthe top rim of vessel 34 where theinner and outer cups 711 and contact each other, they are bonded andsealed so as to provide a hermetically sealed double-walled vessel 34.The space between the inner wall surfaces of the cups "Id and 7ll may befilled with thermal insulation material '72. In the alternative, thespace between the opposing surfaces of cups 70 and 7H may be air filledor they may be evacuated. However, as shown in FIG. 2 the material 72may be foamed thermal insulating material which is suitable for serviceas a thermal shield or insulating substance. The inner cup II may beformed from a relatively thin sheet of magnetic stainless steel.Generally, inner cup 7ll is preferably formed from a material which: ismagnetically permeable; is electrically conductive; has a relativelyhigh electrical resistivity; and, is thermally conductive. Materialsother than stainless steel may be used. Outer cup 7 may, as indicated,be formed from plastic materials, epoxies or polyimides. Moreover, thematerial from which outer cup '70, or a portion thereof, is formed iseither transparent or translucent at a location near the light emittingmeans 64. The purpose for using transparent or translucent material forouter cup 70 will appear hereinafter. Since no substantial heatingcurrent is induced in either counter 22 or in the outer cup 763 ofvessel 34, the material from which the outer cup 70 is formed is notsubjected to elevated temperatures. For example, in the embodiment ofthe vessel shown in FIG. 2, outer cup 70 will be subjected totemperature significantly below 550F. As an alternative material, outercup 7t may be formed from any number of ceramic materials. Again, outercup 70 if formed from ceramic materials should in part be transparent ortranslucent.

The induction coil 36 generates, at ultrasonic frequencies or higher, arapidly changing magnetic field which as indicated in FIG. 2 is coupledbeyond an air gap and beyond the counter 22 so as to intercept the cups70 and '7 ll. Heating currents are induced only in the inner cup 7t;heating currents not being induced in the counter 22 or in the outer cupmember 7% because of thematerials employed. Because induction heating isemployed and the nature of the cooking requirement, the inner cup 71 isnot heated to a temperature higher than 550F. In specifying 550F hereinsome margin for safety is included. Moreover, since no substantialamount of heating current is induced in counter 22 it may be fabricatedfrom materials which are not usable in conventional prior art electricor gas ranges. For example, counter 22 may be fabricated from epoxies,plastics, polyimides, or, as shown in FIG. 2, transparent glass treatedto withstand temperatures of about 5501F. in the embodiment of theinvention illustrated at FIG. 2, counter 22 is also either a transparentmaterial or translucent material which can transmit light. In usingeither a transparent or translucent material for counter 22 theadvantage obtained is that counter 22 may, as a result, have anuninterrupted work surface. However, counter 22 may be fabricated of anopaque material provided an aperture is provided therein fortransmitting light pulses from the vessel 34 to a photodetector unit 54located beneath counter 22.

If required for purposes of electrosatic shielding and- /or structuralenhancement and/or decoration, the counter 22 may also include somemetallic content. However, the inclusion of metallic material in counter22 is necessarily limited to a small amount or larger amounts-sodistributed so as to prevent the formation of ohmic electrical circuitstherein. This is necessary in order to permit substantial quantities ofthe power developed by the induction coil 36 to be coupled with themetallic inner cup 71 of the cooking vessel 34 for the purpose ofheating the cup 71.

A temperature sensing unit in accordance with the present invention iscomprised of a temperature detection unit which is incorporated in thevessel 34 and a temperature receiving uint 50. See FIGS. 2 and 7. Whilethe induction coil 36 produces electromagnetic radiations in theultrasonic, or higher, ranges principally for the purpose ofinducingheating currents in the inner cup 71 of the vessel 34, it also provides,according to the present invention, energy for driving or powering thetemperature detection unit incorporated within the vessel 34. Thisaspect of the invention is described in more detail hereinafter. Sufficeit to state at this point that: one of the important aspects of thepresent invention is the capability of extracting radiatedelectromagnetic power locally within the vessel 34 from the mainmagnetic field generated by the induction coil. The extracted electricalenergy is employable for powering load utilization devices generally.

The various components of the temperature detection unit which areincorporated within the vessel 34 are diagrammatically shown as beingcontained within the dotted line box appropriately labeled in FIG. 7.Similarly, the various components of the temperature receiving unit 50are located within a separate dotted line box which is alsoappropriately labeled in FIG. 7.

Operationally, electromagnetic energy produced by induction coil 36 iscoupled through an air gap and beyond counter 22 into the inner cup 71of the vessel 34. The major portion of this energy so coupled is usedfor inducing heating currents in the cup-like member 71. However, assuggested in the block diagram of FIG. 7, a small portion of thiselectromagnetic energy is coupled to a pick-up coil 60. As shown in FIG.2 the pickup coil 60 is concentrically disposed around a thermistorunit63 in vessel 34. A voltage developed across the pickup coil 60 isdelivered to the input of a rectifier 61. As shown in FIG. 2 rectifier61 is packaged in a small space and located in the vessel 34 between thecups 70 and 71 at a location which is relatively remote from the hotterlower part of the vessel 34. In addition, as indicated at FIG. 2, therectifier 61 is thermally insulated from the inner cup 71 by insulationmaterial 72. Moreover, the rectifier package 61 may be suitably bondedto the outer cup 71 so as to put it in contact with a lower temperaturemedium. Advantageously, the rectifier 61 being so located and insulatedis not subjected to elevated temperatures. The rectifier 61 develops aregulated DC. output which is delivered to the input of a voltagecontrolled oscillator 62 (hereinafter referred to as VCO 62). The VCO 62includes an additional input from a temperature sensor unit 63 which maybe a thermistor unit. As indicated in FIG. 2 the thermistor unit 63 isalso situated in the space between the nested cup members 70 and 71 andis in direct contact with the inner metallic cup 71 for the purpose ofsensing the temperature thereof. An LED (light emitting diode) 64 isconnected to the output of VCO 62 as indicated in FIGS. 3 and 7.Suitably coupled with LED 64 is a lens 640 which acts to collimate thelight emitted from LED 64. As shown in FIG. 2 the LED 64 and lens 64aare located in the space between the nested cups 70 and 71, at thebottom of vessel 34 and against the inside face of the transparent ortranslucent cup 70. Thus, light emitted by LED 64 will be collimated inlens 64a and directed through the transparent or translucent cup member70. Also, as indicated in FIG. 2, VCO 62 is conveniently packaged in asmall space and located near the upper rim of the vessel remotely fromthe bottom surface of the cup member 71 in a relatively cool area of thevessel 34. The VCO 62 may be covered with insulation material 72 and, inthe same manner as rectifier 61, connected to the outer cup so as to bein contact with a lower temperature component.

Briefly, the temperature sensor unit 63 which is in contact with themetallic inner cup 71 changes its resistance or impedance in response tothe temperature of the inner cup member 71. This change in resistance orimpedance of thermistor unit 63 changes the operating voltage of VCO 62and thereby causes VCO 62 to alter its frequency of oscillation inresponse to a voltage change introduced thereto by action of thethermistor unit 63. Thus, there is developed across the LED 64 a signalvoltage of a frequency which varies as a function of the resistance orimpedance of thermistor unit 63. The thermistor unit 63 varies itsimpedance or resistance as a function of the temperature of the cupmember 71. In accordance with the frequency of the signal voltagedeveloped by VCO 62, LED 64 radiates light pulses at a correspondingrate or frequency. The light pulse rate also corresponds to thetemperature of the inner cup 71 as sensed by thermistor unit 63. Thelight pulses produced by LED 64 are conveniently collimated by the lens64a and transmitted through the transparent or translucent cup member 70to the outside of vessel 34 and through the transparent or translucentcounter 22 where they are received by a silicon photodiode 54 or othersuitable photodetector unit, which is part of the temperature receivingunit 50. As suggested in FIG. 2, among other places, the siliconphotodiode 54 or photodetector may conveniently be secured to a lowersurface of counter 22 so as to convert the received light pulses into atrain of electrical signals which are representative of the sensedtemperature of interest. The photodetector unit or silicon photodiode 54is preferably embedded or potted within a suitable matrix of polyimidematerial. Light pulses transmitted to the photodetector 54 from LED 64are converted to electrical signals by the photodetector S4 and thesesignals are delivered to the input of the temperature signal processingcircuit 45. The signal processing circuit 45 includes a gatedmultivibrator which in conjunction with an RC circuit within theprocessing circuit 45 averages the pulses so received whereby thecircuit 45 develops an output signal representative of the temperatureof the vessel 34 as detected by thermistor unit 63. This output signalis delivered to the temperature indicator 30. Thus, for a particulartemperature developed by the inner cup 71 in vessel 34 the thermistor 63has a particular resistance or impedance corresponding to thistemperature. The resistance of thermistor unit 63 causes a voltagechange within VCO 62. The output frequency of VCO 62 is a function ofthis voltage change occasioned by the resistance change of thermistorunit 63. The output frequency developed by VCO 62 is delivered to LED 64which emits a series of light pulses. This series or train of lightpulses changes the conduction periods or on time of photodetector 54.Photodetector 54 effectively modulates" the temperature signalprocessing circuit 45 via a series of signals having conduction periodscorresponding to those of the received light pulses. Thus, thetemperature signal processing circuit 45 is relatively insensitive tointensity of the light pulses inasmuch as it averages the conductiontimes of the various pulses in the pulse train of electrical signalsproduced by photodetector 54. Ultimately the signal processing circuit45 provides an output signal to temperature indicator 30 which isrepresentative of the sensed temperature of interest.

In FIG. 2 for purposes of illustration, the cross sectional dimension ofthe outer cup 70 is shown as being larger than that of inner cup 71.However, it is to be understood that the cross section dimension ofouter cup 70 may be equal to or smaller than the same cross sectionaldimension of the inner cup 71. Also, in FIG. 2 the vessel 34 is shown asbeing provided with feet, such as feet 75, which are molded in the outercup 70. It is to be understood that the inclusion of feet 75 is notabsolutely necessary. However, feet such as the feet 75 are a convenientinnovation in the modified form of the vessel construction hereinafterdiscussed with reference to FIGS. 4 and 5.

The rectifier 61 and VCO 62, as shown in FIG. 2, may be fabricated andpackaged as separate or combined integrated circuits. In one form theseseparated integrated circuits may have the general forms orconfigurations illustrated in FIG. 2. Suffice it to say that: rectifier61 and VCO 62 are preferably in the form of integrated circuits whichhave been miniaturized and packaged accordingly. In FIG. 2 the variouselectrical connections including conductors for the pick-up coil 60,rectifier 61, oscillator 62, thermistor unit 63 and LED 64 areindicated. These conductors may be arranged in the manner suggested inFIG. 2 and embedded in the insulation material 72, which is also adielectric material. In FIG. 3 there is illustrated in the fragmentaryview a modified form of counter 22 of FIG. 2; the counter in FIG. 3being designated as counter 220. As indicated counter 2211 may be of anopaque material and fabricated from a suitable plastic, epoxy orpolyimide as hereinbefore stated. However, inasmuch as light is nottransmittable through the material of counter 22a, it is provided with acentral aperture in which there may be located a plug 22b of lighttransmitting material. Thus the vessel of FIG. 2 may be employed withcounter 22a wherein light pulses developed by the LED 64 are collimatedby lens 64a and transmitted through the outer cup 70 to an air gaplocated be tween the top of counter 22a and the bottom of cup 70; i.e.,in the space external to the vessel 34 which is between the feet 75thereof. The light pulses are eventually transmitted through thetransparent or translucent plug 22b to the photodetector 54.

In FIGS. 4 and 5 there is illustrated another modification of the vesselemployed in the present invention. The vessel shown in FIG. 4 and FIG. 5which is designated, generally, by the reference number 34a is comprisedof an outer cup 70a of opaque material. Materials may be the same asthose chosen for the outer cup 70 of vessel 34 shown in FIG. 2. However,the material 70a may be opaque material or it may be transparent ortranslucent material. The inner cup 71 is a metallic material which isformed from a relatively thin sheet of magnetic stainless steel.Electrically connected, as indicated in FIG. 4, to the inner cup 71 area pair of terminals 80 and 81. In effect, the terminals 80 and 81partially replace the pick-up coil 60 which was a separate component ofthe vessel 34 illustrated in FIG. 2. The terminals 80 and 81 which arespaced apart and con nected to the inner cup 71 of vessel 34a havedeveloped therebetween a voltage drop, or IR drop, caused by thecirculating currents in the inner cup 71. These circulating currents areinduced in the metallic cup member 71 by the main magnetic fieldproduced by induction coil 36. The terminals 80 and 81 beingelectrically connected with the cup 71 in spaced apart relation thereonhave a voltage drop developed thereacross due to the circulatingcurrents and the voltage appearing between terminals 80 and 811 is usedas the input to the rectifier 61. This is also illustrateddiagrammatically at FIG. 8 whereat the terminals 80) and fill havedeveloped therebetween the voltage e Except for the absence of thepick-up coil 60, for which the terminals 80 and 81 have been substitutedas a voltage source, the other internal components of the vessel 340 arethe same as'those employed with the vessel 34 shown in FIG. 2.Operationally, the system of FIG. 4 operates in the same manner ashereinbefore described with reference to FIG. 7 with the exception thatthe input voltage e as shown in FIG. 8 is used to drive rectifier 61.

Another important feature of the vessel 34a is better illustrated in theenlarged fragmentary diagram of FIG. 5. Secured to theouter cup a, whichin the embodi ment shown is an opaque cup, is a fiber optic means 90.For the purpose of more evenly distributing the light pulses emitted bythe LED 64 there is optically coupled with the collimating lens 64a afiber optic bundle 90. A small aperture through the bottom of the outercup 70a is provided so as to optically couple a fiber optic bundle 90awith collimating lens 64a. Coupled with and securedto this bundle 90a isa spirally wound fiber optic ribbon 90 which carries and evenlydistributes the light emitted from LED 64 via lens 64a and bundle 90a.As indicated in FIG. 4 this ribbon is spirally wound so as to provide apancake-like form or-disk which covers a substantial area on the outsidesurface of the bottom of vessel 34a; i.e., the spiral wound fiber opticribbon 90 being disposed between the feet 75 of the outer cup 70a. Thus,evenly distributed light is transmitted through the fiber optic ribbon90 and through the transparent counter 22 to the photodetector 54 asindicated in FIG. 5. As an alternative construction the counter 22a maybe employed which may also include a large diameter aperture foraccommodating a larger diameter transparent or translucent plug 22b.

FIG. 6 is a graphical representation showing the relationship betweentemperature sensed by thermistor 63 as a function of the frequency orrepetition rate of the light pulses emitted by LED 64.

In FIG. 9 there is shown a voltage source which may be the same voltagesource as developed between the terminals and 81 in FIG. 8 or it may bethe output of the pick-up coil 60. Coupled to the voltage e in FIG. 9 isa load utilization means which may be operated from the voltage e.Advantageously, power developed by the changing magnetic field producedby the main induction coil 36 as coupled into the vessel may,ultimately, be extracted as a voltage e either by a pick-up coil such as60 or through an IR drop developed between terminals such as 80 and 81for the purpose of providing local power or energy in the vessel foroperating stirring means or other auxiliary devices requiring smallamounts of power. The present invention illustrates one, among manysituations where the extracted voltae e may be employed for developingsignal energy as to temperature data.

Advantageously, the LED 64 employed produces monochromatic light so thatfilters are not required in conjunction with photodetector 54. Moreover,because of the inertialess characteristic of LED 64, as compared withother light sources (e.g., filamentary sources and glow sources), it canproduce detectable light pulses at a band in the megahertz range. Hence,the very high frequency light pulses are easily discriminated by thephotodetector 54 from stray interference sources such as ambient light(e.g., incandescent and fluorescent fixtures as well as sunlight). Also,of course, no interference with light pulse discrimination is occasionedby the induction coil which operates in the kilohertz range and is,ofcourse, a non-optical device.

The control scheme herein disclosed can be interlocked with theinduction surface control circuitry disclosed in, among others, thepatent applications hereinbefore cross referenced.

Another very important aspect of the invention is that the voltages eand e of FIGS. 8 and 9, respectively, allow for use ofintegratedcircuits for the various components. This is so because e ande are optimized at 30 volts or less. The same advantage obtains for theinduced voltage produced by pick-up coil 60 in the other embodimentsdisclosed.

Thus, hereinbefore described by way of illustrative embodiments thereofis an induction cooking or warming appliance which includes togetherwith a novel ves sel a temperature sensing unit which is free from thespurious heating encountered in prior art electric and gas ranges. Inthis regard the nature of the heating source does not produce the sameelevated temperatures at the same locations or within the samecomponents. For example the induction coil 36 induces heating currentsin the cup 71 rather than in the vessel support or counter 22. Thetemperature detection unit which is located within the vessel and thetemperature receiving unit 50 are located in regions of relatively lowmagnetic intensity. Also the thermistor unit 63 has a resistance of theorder of 10 ohms so that, at best, only insignificant heating currentsare induced therein. Also the thermistor leads may be twisted for thepurpose of cancelling induced voltages. The various electroniccomponents incorporated within the vessel and under the counter are notsubjected to a temperature as high as the specification temperature of550F. Certainly these components are not subjected to the elevatedtemperatures of l,600F which occur at certain regions in prior artelectric and gas ranges. In this regard the present invention disclosesthat the electronic components 60, 61, 62 and 64 are surrounded bythermal insulation 72 and some or all of these components may beremotely located from the element 71 which is heated and at a moreelevated temperature. In addition to locating the aforesaid componentsremotely from higher temperature regions in the vessel, they may also bethermally connected to the outer cup members surface and hence to alower temperature environment, or "sink."

Benefically, with the present invention the materials of fabrication ofthe temperature sensing unit (temperature detection unit and componentsas well as the temperature receiving unit and components) are notrestricted by the elevated temperatures encountered with the prior artelectric and gas ranges. Hence, many materials such as plastics,epoxies, polyimides are usable in the practice of the present invention.Moreover, because there is no heat source as in prior art rangeshereinbefore described and because of the location of the variouscomponents of temperature detection and temperature receiving units,these components need not be thermally shielded or insulated in the waysor to the extent employed in prior art electric and gas ranges. With thetemperature sensing unit employed in the present invention, an accuratesensing of the temperature of the vessel may be achieved. This may bedone regardless of the weight of the vessel and further without regardto whether the outside surface of the vessel has an irregular surface orcontour. Moreover, with the temperature sensing unit provided herein theprior art spring construction or arrangement is not required. Nor wouldsprings be of any use in connection with temperature sensing aspracticed with the present invention. Another advantageous aspect of thesubject invention is that the counter 22 or vessel supporting means mayhave, if desired, an uninterrupted working surface on the top thereof.

Another important advantage of the present invention is that temperaturedata may be transmitted by wireless means in the form of light pulses toa location which can be relatively remote from the cooking or warmingarea.

Although the invention has been described and illustrated by means ofspecific embodiments thereof, it is, nevertheless, to be understood thatmany changes in materials, details of construction and in thecombination and arrangement of parts or components may be made withoutdeparting from the spirit of the invention, the scope of which isdefined in the claims hereinafter set forth.

What is claimed is:

1. In combination, an induction heating appliance and a vessel; saidappliance comprising vessel supporting means for supporting said vessel,said supporting means having no substantial heating current inducedtherein when subjected to a changing magnetic field, an induction coilenergizable for producing a main changing magnetic field, means forenergizing said coil with electric power, and a temperature receivingunit included in said appliance; said vessel comprising a portion inwhich heating current is induced by said main changing magnetic fieldwhen said vessel is supported by said supporting means, and atemperature detection unit supported by said vessel, said temperaturedetectionunit including a temperature sensor unit for sensing thetemperature of said vessel, said temperature detection unit beingenergizable by said main changing magnetic field to produce light pulsesrepresentative of a temperature corresponding to the temperature sensedby said temperature sensor unit, said temperature receiving unitincluding means responsive to said light pulses for producing a signalrepresentative of the temperature sensed by said temperature sensorunit.

2. The combination according to claim 1 wherein said portion of saidvessel is provided with a pair of terminal means between which there isdeveloped a voltage corresponding to the voltage drop developed by theheating currents induced in said portion by the main field of saidinduction coil, said voltage developed between said terminal meansenergizing said temperature detection unit.

3. The combination according to claim 1 wherein said temperaturedetection unit supported by said vessel is further comprised ofa pick-upcoil for developing a first voltage when subjected to said main changingmagnetic field, a rectifier for converting said first voltage to arectified second voltage, a voltage controlled oscillator energized bysaid second voltage for producing a variable frequency output signal,said temperature sensor unit providing an impedance corresponding to atemperature sensed by said sensor unit, said temperature sensor unitbeing electrically coupled with said voltage control oscillator wherebysaid oscillator produces an output signal of a frequency correspondingto the temperature sensed by said sensor unit, and a light emittingdiode electrically coupled with said voltage controlled oscillator forproducing light pulses at a rate corresponding to said output signalproduced by said oscillator.

4. An inductively heatable vessel comprising: a first metallic wallmember and a second non-metallic lighttransmitting wall member, saidwall members having portions thereof sealed together to form a sealeddouble-walled vessel having an enclosed space between said wall members,said first wall member forming an inside wall surface of said vessel,said first wall member having heating current induced therein when saidfirst wall member is subjected to a changing magnetic field, atemperature detection unit located within said space between said wallmembers, said temperature detection unit comprising a temperature sensorunit for sensing the temperature of at least said first wall member andlight emitting means energizable for producing light pulsesrepresentative of the temperature sensed by said sensor unit, said lightpulses being transmitted through said second wall member.

5. The vessel according to claim 4 wherein said temperature detectionunit is comprised of a pick-up coil, a rectifier, an oscillator and saidlight emitting means, said pick-up coil producing a first voltage inresponse to said changing magnetic field to which said first wall memberis also subjected, said rectifier producing from said first voltage arectified voltage, said oscillator being driven by said rectifiedvoltage and producing a variable frequency output signal correspondingto a temperature sensed by said temperature sensor unit, said lightemitting means, in response to the output signal produced by saidoscillator, producing light pulses at a frequency corresponding to theoutput frequency of said oscillator and representing the temperaturesensed by said sensor unit.

6. The vessel according to claim 4 wherein said first wall memberincludes a pair of terminal means between which a voltage difference isextractable, said voltage difference being produced by the voltage dropproduced by the induced current flowing in said first wall member, saidvoltage difference being electrically coupled with said temperaturedetection unit for energizing said light emitting means.

7. In combination, an inductively heatable vessel and a temperaturereceiving unit located remotely from said vessel, said vessel comprisinga first metallic wall member and a second non-metallic wall member, saidwall members having portions thereof sealed together to form adouble-walled vessel having an enclosed space between said walledmembers, said first metallic wall member forming the inside surface ofsaid vessel, said first wall member being adapted for having heatingcurrent induced therein when subjected to a changing magnetic field, atemperature detection unit located within said space between said wallmembers, said temperature detection unit including a temperature sensorunit for sensing the temperature of at least said first wall member,said temperature detection unit including means for producing lightpulses containing data representative of the temperature sensed by saidtemperature sensor unit, said vessel having filter optic means opticallycoupled with said light pulse producing means for transmitting the lightpulses to said temperature receiving unit.

8. The combination according to claim 7 wherein said remotely locatedtemperature receiving unit includes a photodetector optically coupledwith said light pulses for producing an electrical signal therefromrepresentative of the temperature sensed by said temperature sensor unitof said temperature detection unit, a temperature signal processingcircuit for processing the signal from said photodetector to produceanother signal representative of said temperature sensed by saidtemperature sensor unit, and display means coupled with said temperaturesignal processing circuit for indicating the temperature sensed by saidtemperature sensor unit.

9. in combination, an induction cooking appliance and a cooking vessel,said appliance comprising vessel supporting means in which nosubstantial heating current is induced when subjected to a changingmagnetic field, an induction coil energizable for producing a mainchanging magnetic field, means for energizing said induction coil withelectric power of at least ultrasonic frequency, and a temperaturereceiving unit supported by said appliance, said vessel comprising afirst metallic wall member and a second non-metallic wall member, saidwall members having portions thereof sealed together to form adouble-walled vessel with an enclosed space between said wall members,said first metallic wall member forming the inside surface of saidvessel and being adapted for containing foodstuff to be cooked, saidfirst wall member also being adapted for having heating current inducedtherein when said vessel is supported by said vessel supporting meanssuch that said first wall member of said vessel is subjected to saidmain changing magnetic field, a temperature detection unit locatedwithin said space between said wall members, said temperature detectionunit including a temperature sensor unit for sensing the temperature ofat least said first metallic wall member, said temperature detectionunit being energizable by said main changing magnetic field to producelight containing temperature data corresponding to the temperaturesensed by said temperature sensor unit, said temperature receiving unitsupported by said appliance including means responsive to said producedlight for produc ing a signal representative of the temperature sensedby said temperature sensor unit.

10. The combination according to claim 9 further comprising displaymeans responsive to the signal produced by said temperature receivingunit for indicating the temperature sensed by said temperature sensorunit.

11. The combination according to claim 9 wherein said vessel supportingmeans transmits light and wherein the light produced by said temperaturedetection unit is transmitted through said vessel supporting means tosaid temperature receiving unit.

electrical current is induced in said wall member by action of thechanging magnetic field; spaced-apart electrical terminal means,electrically connected to said wall member at different locationsthereon, for provid' 7 ing therebetween a voltage approximately equal tothe voltage drop between said different locations caused by inducedcurrent between said different locations in said wall member; and, loadmeans supported by said vessel for utilizing said voltage.

1. In combination, an induction heating appliance and a vessel; saidappliance comprising vessel supporting means for supporting said vessel,said supporting means having no substantial heating current inducedtherein when subjected to a changing magnetic field, an induction coilenergizable for producing a main changing magnetic field, means forenergizing said coil with electric power, and a temperature receivingunit included in said appliance; said vessel comprising a portion inwhich heating current is induced by said main changing magnetic fieldwhen said vessel is supported by said supporting means, and atemperature detection unit supported by said vessel, said temperaturedetection unit including a temperature sensor unit for sensing thetemperature of said vessel, said temperature detection unit beingenergizable by said main changing magnetic field to produce light pulsesrepresentative of a temperature corresponding to the temperature sensedby said temperature sensor unit, said temperature receiving unitincluding means responsive to said light pulses for producing a signalrepresentative of the temperature sensed by said temperature sensorunit.
 2. The combination according to claim 1 wherein said portion ofsaid vessel is provided with a pair of terminal means between whichthere is developed a voltage corresponding to the voltage drop developedby the heating currents induced in said portion by the main field ofsaid induction coil, said voltage developed between said terminal meansenergizing said temperature detection unit.
 3. The combination accordingto claim 1 wherein said temperature detection unit supported by saidvessel is further comprised of a pick-up coil for developing a firstvoltage when subjected to said main changing magnetic field, a rectifierfor converting said first voltage to a rectified second voltage, avoltage controlled oscillator energized by said second voltage forproducing a variable frequency output signal, said temperature sensorunit providing an impedance corresponding to a temperature sensed bysaid sensor unit, said temperature sensor uNit being electricallycoupled with said voltage control oscillator whereby said oscillatorproduces an output signal of a frequency corresponding to thetemperature sensed by said sensor unit, and a light emitting diodeelectrically coupled with said voltage controlled oscillator forproducing light pulses at a rate corresponding to said output signalproduced by said oscillator.
 4. An inductively heatable vesselcomprising: a first metallic wall member and a second non-metalliclight-transmitting wall member, said wall members having portionsthereof sealed together to form a sealed double-walled vessel having anenclosed space between said wall members, said first wall member formingan inside wall surface of said vessel, said first wall member havingheating current induced therein when said first wall member is subjectedto a changing magnetic field, a temperature detection unit locatedwithin said space between said wall members, said temperature detectionunit comprising a temperature sensor unit for sensing the temperature ofat least said first wall member and light emitting means energizable forproducing light pulses representative of the temperature sensed by saidsensor unit, said light pulses being transmitted through said secondwall member.
 5. The vessel according to claim 4 wherein said temperaturedetection unit is comprised of a pick-up coil, a rectifier, anoscillator and said light emitting means, said pick-up coil producing afirst voltage in response to said changing magnetic field to which saidfirst wall member is also subjected, said rectifier producing from saidfirst voltage a rectified voltage, said oscillator being driven by saidrectified voltage and producing a variable frequency output signalcorresponding to a temperature sensed by said temperature sensor unit,said light emitting means, in response to the output signal produced bysaid oscillator, producing light pulses at a frequency corresponding tothe output frequency of said oscillator and representing the temperaturesensed by said sensor unit.
 6. The vessel according to claim 4 whereinsaid first wall member includes a pair of terminal means between which avoltage difference is extractable, said voltage difference beingproduced by the voltage drop produced by the induced current flowing insaid first wall member, said voltage difference being electricallycoupled with said temperature detection unit for energizing said lightemitting means.
 7. In combination, an inductively heatable vessel and atemperature receiving unit located remotely from said vessel, saidvessel comprising a first metallic wall member and a second non-metallicwall member, said wall members having portions thereof sealed togetherto form a double-walled vessel having an enclosed space between saidwalled members, said first metallic wall member forming the insidesurface of said vessel, said first wall member being adapted for havingheating current induced therein when subjected to a changing magneticfield, a temperature detection unit located within said space betweensaid wall members, said temperature detection unit including atemperature sensor unit for sensing the temperature of at least saidfirst wall member, said temperature detection unit including means forproducing light pulses containing data representative of the temperaturesensed by said temperature sensor unit, said vessel having filter opticmeans optically coupled with said light pulse producing means fortransmitting the light pulses to said temperature receiving unit.
 8. Thecombination according to claim 7 wherein said remotely locatedtemperature receiving unit includes a photodetector optically coupledwith said light pulses for producing an electrical signal therefromrepresentative of the temperature sensed by said temperature sensor unitof said temperature detection unit, a temperature signal processingcircuit for processing the signal from said photodetector to produceanother signal representative of said tempeRature sensed by saidtemperature sensor unit, and display means coupled with said temperaturesignal processing circuit for indicating the temperature sensed by saidtemperature sensor unit.
 9. In combination, an induction cookingappliance and a cooking vessel, said appliance comprising vesselsupporting means in which no substantial heating current is induced whensubjected to a changing magnetic field, an induction coil energizablefor producing a main changing magnetic field, means for energizing saidinduction coil with electric power of at least ultrasonic frequency, anda temperature receiving unit supported by said appliance, said vesselcomprising a first metallic wall member and a second non-metallic wallmember, said wall members having portions thereof sealed together toform a double-walled vessel with an enclosed space between said wallmembers, said first metallic wall member forming the inside surface ofsaid vessel and being adapted for containing foodstuff to be cooked,said first wall member also being adapted for having heating currentinduced therein when said vessel is supported by said vessel supportingmeans such that said first wall member of said vessel is subjected tosaid main changing magnetic field, a temperature detection unit locatedwithin said space between said wall members, said temperature detectionunit including a temperature sensor unit for sensing the temperature ofat least said first metallic wall member, said temperature detectionunit being energizable by said main changing magnetic field to producelight containing temperature data corresponding to the temperaturesensed by said temperature sensor unit, said temperature receiving unitsupported by said appliance including means responsive to said producedlight for producing a signal representative of the temperature sensed bysaid temperature sensor unit.
 10. The combination according to claim 9further comprising display means responsive to the signal produced bysaid temperature receiving unit for indicating the temperature sensed bysaid temperature sensor unit.
 11. The combination according to claim 9wherein said vessel supporting means transmits light and wherein thelight produced by said temperature detection unit is transmitted throughsaid vessel supporting means to said temperature receiving unit.
 12. Avessel comprising: at least one wall member defining a storage spaceadapted for receiving material to be heated by transfer of heat fromsaid wall member to the received material, said wall member beingcomprised of material in which electrical current is induced when saidwall member is subjected to a changing magnetic field, said material ofsaid wall member having an electrical resistivity of sufficientmagnitude to enable the development of significant electrical power insaid wall member for dissipation in the form of heat when electricalcurrent is induced in said wall member by action of the changingmagnetic field; spaced-apart electrical terminal means, electricallyconnected to said wall member at different locations thereon, forproviding therebetween a voltage approximately equal to the voltage dropbetween said different locations caused by induced current between saiddifferent locations in said wall member; and, load means supported bysaid vessel for utilizing said voltage.